| Term | Definition / Meaning / Stand for |
| ac |
Acre (Area) |
| ac-ft |
Acre-Foot (Volume) |
| acr-in |
Acre-Inch (Volume) |
| A/kg |
Ampere per Kilogram (Charge-to-Mass Ratio) |
| A/m |
Ampere per Meter (Magnetic Field) |
| A/(m·s) |
Ampere per Meter per Second (Electromagnetic Wave) |
| A/(Ω·m) |
Ampere per Ohm per Meter (Electric Conductivity) |
| AΩ |
Ampere-Ohm (Voltage) |
| A·s |
Ampere-Second (Electric Charge) |
| amp-turn |
Ampere-Turn (Magnetic Force) |
| As |
Ampere-second (Charge) |
| ang |
Angstrom (Length) |
| arb. unit |
Arbitrary Unit (General) |
| arcdeg |
Arcdegree (Angle) |
| arcmin |
Arcminute (Angle) |
| arcsec |
Arcsecond (Angle) |
| atm-cm |
Atmosphere-Centimeter (Pressure-Length) |
| atU |
Atomic Unit (Physics) |
| au |
Atomic Unit of Length |
| aCd |
Attocandela (Luminous Intensity) |
| aCi |
Attocurie (Radioactivity) |
| ad |
Attoday (Time) |
| adp |
Attodegree per Second (Angular Velocity) |
| aF |
Attofarad (Capacitance) |
| ag |
Attogram (Mass) |
| aH |
Attohenry (Inductance) |
| aJ |
Attojoule (Energy) |
| aK |
Attokelvin (Temperature) |
| aL |
Attoliter (Volume) |
| attom |
Attometer (Length) |
| am |
Attometer (Length) |
| amol |
Attomole (Amount of Substance) |
| aN |
Attonewton (Force) |
| aΩ |
Attoohm (Resistance) |
| aΩ·m |
Attoohm-Meter (Resistivity) |
| aPa |
Attopascal (Pressure) |
| apd |
Attopascal-Day (Pressure-Time) |
| as |
Attosecond (Time) |
| ast |
Attostere (Volume) |
| aT |
Attotesla (Magnetic Flux Density) |
| at |
Attotonne (Mass) |
| aV |
Attovolt (Voltage) |
| aV/m |
Attovolt per Meter (Electric Field Strength) |
| aW |
Attowatt (Power) |
| aWb |
Attoweber (Magnetic Flux) |
| AABA |
Adams Avenue Business Association |
| AMLR |
Adelaide and Mount Lofty Ranges |
| ALRS |
Admiralty List of Radio Signal |
| ACH |
Air Changes per Hour |
| ADFC |
Allgemeinen Deutschen Fahrrad Clubs |
| A |
Ampere (Electric Current) |
| A |
Ampere |
| Amp |
Ampere |
| Ah |
Ampere hour |
| Ah |
Ampere-hour (Electric Charge) |
| A |
Angstrom |
| AUROC |
Area under receiver operating characteristic |
| AU |
Astronomical Unit (Distance) |
| atm |
Atmosphere (Pressure) |
| amu |
Atomic Mass Unit (Mass) |
| amol |
Attomole |
| AMW |
Average Molecular Weight |